The present invention relates to a photo conductive device, more specifically, the present invention relates to a photo conductive device of low exhausting power""s point light source which can produce top light source of uniform brightness.
Ever since liquid crystal display, LCD, is invented, the impossible mission of portable computer comes true. Since liquid crystal does not light itself, so there usually has a backlight device with backlighting function as the light source to achieve the purpose of displaying images on the LCD. In the present, LCD is used mainly on notebook, besides, it is also used on the monitors of small TV, video, PDA and cellular phone.
Traditional backlight device can be referred to the following R.O.C. patents: application No. 85100566, 88110209 and 84206661. Take FIG. 1 as example, the principle of backlight device is simply mentioned as below: firstly, the light source 2 inside the backlight device shoots the light to the reflecting slice 6 of the bottom of the photo conductive plate 4 which is previous to light. Then the reflecting slice 6 reflects the light to the diffusing film 8 which is on the bottom of the photo conductive plate 4 and above the reflecting slice 6. After that, the diffusing film 8 diffuses the light and then the diffused light penetrates the photo conductive plate 4 to inject to the LCD 10 which is above the photo conductive plate 4 with uniform brightness. The diffusing slice 12 between the photo conductive plate 4 and the LCD 10 is used to prevent the formation of image of the backlight device from being displayed on the LCD 10.
There are two kinds of light sources used for current backlight device: point light source and line light source. Point light source mostly lights by LED, and line light source mostly lights by cold cathode tube. Currently seen in the market of full color portable cellular phone, PDA use mostly cold cathode tube light source, which will easily produce top light source with uniform brightness, but the exhausting power is very huge. However, the exhausting power of the single color top light source which lights by LED is far smaller than the exhausting power of the line light source which lights by cold cathode tube, but the uniform brightness of the single color top light source is worse than the uniform brightness of line light source.
As a result, the principle of this invention is how to make backlight device of point light source using low exhausting power to produce top light source with uniform brightness.
The purpose of this invention is to provide a backlight device of low exhausting power""s point light source which can produce top light source of uniform brightness, as to decrease the production cost and exhausting power rate of the backlight device.
This invention provides a backlight device which includes at least: a photo conductive plate used for visible light to go through; a point light source, which is beside the photo conductive plate, used for producing visible light; a first diffusing top, which is beside the photo conductive plate, used for diffusing the visible light from the point light source to the lighting method of uniform line light source; a second diffusing top, which is on the bottom of the photo conductive plate, used for diffusing the visible light from the first diffusing top to the lighting method of uniform top light source; a diffusing reflect objective, which is below the photo conductive plate, used for diffusing the light and then reflecting the diffused light to the photo conductive plate.
The backlight device mentioned above further includes a diffusing slice, which is above the photo conductive plate and below a LCD, is used to prevent the formation of image of the backlight device below the diffusing slice from being displayed on the LCD. The point light source includes using LED to light. The 1st diffusing top and the 2nd diffusing top are made up of diffusing material or micro-structure, wherein the 1st diffusing top and the 2nd diffusing top are used for light to transfer uniformly. The micro-structure shape of the 1st diffusing top includes circle, ellipse or square. The micro-structure shape of the 2nd diffusing top includes V shape or circle. Besides, there is an air gap between the photo conductive plate and the 1st diffusing top, wherein the air gap is used for transferring the visible light of the point light source to the lighting method of line light source (or named as rectification action). Also, wherein the diffusing reflect objective includes the diffusing reflect slice or white color bottom frame. The location of the point light source is in front and below the photo conductive plate.